(1) Field of the Invention
This invention relates to an image forming apparatus that forms an image made of toner such as a printer, a copy machine, or a multifunction machine having plural functions, and particularly to an image forming apparatus suitable for retrieving the toner remaining on an image carrier because of transfer failure or the like at the time of the image formation and effectively reusing a proper quantity of the retrieved toner.
(2) Description of the Related Art
In an image forming apparatus that forms an image using toner as a developer, since toner remains on an image carrier, an intermediate transfer member and the like because of transfer failure or the like at the time of the image formation, removal of the toner by a cleaning device, recirculation of the toner to a developing device and reuse of the toner have been attempted.
For example, in order to address the problem of continuous increase of retrieved toner with the lapse of time while retrieving toner remaining on an image carrier by a cleaner unit and effectively reusing the retrieved toner, the present applicant has previously proposed an image forming apparatus having a waste toner housing unit that houses the toner retrieved by the cleaner unit and carried by a second carrier unit, and a control unit that controls the supply ratio of unused toner and retrieved toner supplied to a developing unit in accordance with a cumulative value of pixel count of image information.
Also, in order to properly process retrieved toner even when the quantity of retrieved toner supplied from a cleaning device exceeds the processing capacity of a classifying device in an image forming apparatus having a toner recycle classifying device that classifies impurities from toner retrieved by the cleaning device, there has been proposed an image forming apparatus having an excessive retrieved toner processing unit that is arranged near the classifying unit and processes excessively supplied retrieved toner, and a quantifying wall that is arranged between the classifying unit and the excessive retrieved toner processing unit and causes the quantity of retrieved toner exceeding the processing capacity of the classifying device to overflow to the excessive retrieved toner processing unit.
However, these proposed image forming apparatuses have the following problems.
In the former image forming apparatus, the second carrier unit that carries the retrieved toner to the waste toner housing unit is provided in the state of being branched from the cleaning unit, and the second carrier unit is driven while its operation is controlled. Therefore, the structure of the apparatus is complicated accordingly. Also, since the operation to carry the retrieved toner to the waste toner housing unit need to be controlled, the control operation is complicated. Moreover, since the quantity of the retrieved toner to be supplied to the developing unit is controlled in accordance with the cumulative value of pixel count or the like, the control operation is further complicated. Such complexity may be increased further when applied to a color image forming apparatus in which plural image carriers are arranged.
On the other hand, in the latter image forming apparatus, measures to prevent clogging or the like and maintenance and inspection of the classifying unit are necessary. Also, the structure of the classifying unit itself is complicated and large-scaled. Moreover, since the quantity of the classified retrieved toner to be supplied to the developing unit is not particularly adjusted, the rate of use of the retrieved toner increases and may cause occurrence of defective image quality such as image fog. Furthermore, there is another problem that the quantity of the retrieved toner to be supplied to the developing unit depends on the processing capacity of the classifying unit.